The common marmoset (Callithrix jacchus) is becoming an increasingly important biomedical research model in neuroscience, aging and infectious disease. Due to its small size, fast maturation, and high fertility, this species is particularly prized for research into aging, gene editing and transgenic production. There is clear evidence of unmet demand for marmosets by the US research community, pointing to the value of increasing marmoset production. The Southwest National Primate Research Center (SNPRC) has the trained personnel and infrastructure in place to effectively and efficiently breed additional marmosets. Of particular importance, we have the largest population of marmosets in the US and can, therefore, most rapidly expand the breeding population without encountering the issue of having to search elsewhere for additional animals to put into breeding. However SNPRC is limited in the extent to which we can expand production by appropriate housing space, caging and support to shunt animals away from sales and research and into breeding. We therefore are requesting support for: (1) Housing Space. While the center has more than adequate land for expansion, we do require additional, appropriate indoor housing in order to expand production. The most expedient way to increase production capacity is the placement of a custom-designed modular building in association with our other marmoset housing. The proposed modular building would provide approximately 1,008 sq ft of additional animal housing space, increasing our housing space for production by approximately 75%. (2) Caging. Our rationale for the marmoset caging request is to both increase our capacity to house this species but, perhaps more importantly, to provide us with flexible caging options that can be used for pair-housing, small group housing or large group housing. We project that the support provided by this supplement would allow us within 2.5 years to support 64 breeding units as opposed to the 36 we presently support, increasing our weaned production per year from 90-110 animals to 160-192 animals - an approximately 75% increase. This will position SNPRC to rapidly increase production, if mechanisms of support for moving marmosets from sales or research into breeding become available in the coming year.